This invention relates to the production of molded soft contact lenses. More particularly, the invention relates to polypropylene contact lens molds and methods of making soft contact lenses, such as hydrogel contact lenses, using such molds.
Morrill U.S. Pat. No. 5,843,346 discloses a method of cast molding rigid gas permeable (RGP) contact lenses employing mold sections made of a thermoplastic polyolefin resin, such as polypropylene resin, having a melt flow rate of at least about 21 g/10 min. This patent discloses that mold sections made of such high melt flow rate resins produce rigid contact lenses with a higher consistency of optical quality relative to mold sections injection-molded from other thermoplastic polyolefin resins, i.e., thermoplastic polyolefin resins having a melt flow rate of 20 g/10 min or lower.
Portnoy et al. U.S. Patent Publication No. 2004/0044106 refers to the above-noted Morrill patent and (RGP) contact lenses. This publication discloses the use of molds including nucleated, metallocene-catalyzed polypropylene with melt flow rates lower than 100 g/10 min, desirably lower than 21 g/10 min, and including a nucleating agent. Melt flow rates of the polypropylene polymers were measured according to ASTM D1238 at 230° C., with a 2.16 kg load. Portnoy et al. disclose that such molds are useful for precision applications, such as molds for (RGP) contact lenses. Portnoy et al. focuses on the details of making the nucleated, metallocene catalyzed polypropylene and does not disclose contact lenses other than rigid gas permeable (RPG) contact lenses. Moreover, Portnoy et al. does not disclose any particular benefits or advantages of contact lenses produced using nucleated, metallocene-catalyzed polypropylene molds.
Ansell U.S. Patent Publication No. 2006/0051454 discloses the use of molds made from Ziegler-Natta catalyst-based polyolefin resin having a melt flow rate of less than 21 g/10 min, as per ASTM D 1238, to produce soft contact lenses. The Ansell publication discloses that molds made of the Ziegler-Natta polyolefin resin molds with a melt flow rate less than 21 g/10 min have equivalent or better quality indications relative to molds created with metallocene catalyst-based polypropylene, and that lenses produced using a polyolefin mold material with a melt flow index of less than 21 g/10 min can include a diminished number of holes, chips, and tears in the manufactured lenses. The Ansell publication does not disclose or suggest the use of a nucleating agent.
There is a continuing need to provide contact lenses, for example, soft or hydrogel contact lenses, with good surface and optical properties in a consistent and cost effective manner.